Thin film alloy disks for vertical magnetic recording typically comprise a substrate, a magnetic or nonmagnetic underlayer and a magnetic layer having an ordered crystalline formation with its easy axis of magnetization oriented generally perpendicular to the substrate. One type of material used as the magnetic layer is a cobalt-chromium (CoCr) alloy which is sputter-deposited to form a film having a hexagonal close packed (hcp) crystalline structure with the [00.2] axis (the C-axis) oriented perpendicular to the disk substrate.
The magnetic properties of thin film alloy disks made with various substrates, a titanium underlayer and a CoCr perpendicular magnetic layer are described by Kobayashi, et al. in "High Density Perpendicular Magnetic Recording on Rigid Disks", Fujitsu Scientific and Technical Journal, Vol. 19, No. 1, pp. 99-126, March, 1983. That article discloses that substantially improved perpendicular magnetic anisotropy of the CoCr film is achieved with the use of a titanium (Ti) underlayer, and suggests that the C-axis orientation of the CoCr film is improved because the titanium underlayer isolates the influence of the substrate from the CoCr film. The CoCr magnetic films described by Kobayashi, et al showed a C-axis dispersion, as measured by the half value width, .DELTA..theta..sub.50, of an x-ray reflection rocking curve, of between 7.degree. and 9.degree.; a perpendicular coercive force, H.sub.c.perp., of 475 Oersted (Oe); and a horizonal coercive force H.sub.c.parallel. of 312 Oe. The Kobayashi article also discloses a nickel-iron (NiFe) soft magnetic layer between the substrate and the titanium underlayer to provide a magnetic flux return path.
A thin film alloy disk having a nonmagnetic cobalt-tantalum (CoTa) alloy as an underlayer for a CoCr perpendicular magnetic layer is disclosed in Japanese published unexamined patent application 59-77620 assigned to Suwa Seikosha Co., Ltd.
Published European Patent application No. 93838 assigned to Teijin, Ltd. discloses a disk for vertical magnetic recording having a soft magnetic underlayer of an amorphous CoTa alloy and a magnetic layer of CoCr with perpendicular magnetic anisotropy. This reference also discloses the addition of tantalum to provide a ternary alloy of CoCrTa as the magnetic layer over the CoTa amorphous magnetic underlayer.
The magnetic properties of a vertical recording disk with an 8000 Angstrom CoCrTa magnetic layer deposited on a 1000 Angstrom Cr underlayer are described by Langland and Albert in "Recording on Perpendicular Anisotropy Media with Ring Heads", IEEE Transactions on Magnetics, Vol. MAG-17, No. 6, November, 1981, pp. 2547-2549.